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Old 03-30-2011, 01:56 AM
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Question A4 1.8T cold start problem - low rpm

When my A4 B5 1.8T sits for 10 hours or longer, it needs quite a few cranks (10 seconds or so) until it starts. Even then, it starts slowly and rough.

When it was working fine, rpms would go higher in the first minute after a cold start, bu it no longer does that. Almost like a missing "choke" - or whatever the equivalent is for these engines.

Do you know what controls the rpm increase for a cold engine? What could cause them to stay low like it would be for a warm engine?

I already cleaned the MAF, replaced fuel filter + spark plugs. Temp display is fine otherwise, but I'll try replacing the sensor next.
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Old 03-30-2011, 11:09 AM
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On the first start of the day mine idles low as well. Any other cold start (but not the first start in a long period of time such as an overnight) it will idle high, as it should, for about a minute.

No clue what this is all about either...
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Old 04-03-2011, 02:08 AM
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Swapping out the coolant temp sensor fixed my cold start problem.

I didn't think it would since the temp gauge showed correct values, but maybe it's driven by another sensor.
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Old 04-03-2011, 03:58 PM
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Does the idle surge?
What is a "high" idle for you?

Cold start mine will be about 850 all day long. Warm start again,850. My coolant temp gauge is shot and no starting problems.

I would definitely check the sensor governing the intake air temp and maybe check 02's? Could be something simple, could be...lol

Another thing to check are vacuum lines!!!
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Old 04-03-2011, 11:42 PM
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shot in the dark but

Starter solenoid? Starter Motor? Loose wiring in the starting circuit?

Like wise, mine starts in 2-3 seconds and idles at 850 hot/cold
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Old 04-04-2011, 01:48 AM
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Replace the hall sender / crank position sensor. Usually when these sensors are cold, they have less electrical resistance, while warm they may function well but not when cold.
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Old 04-04-2011, 02:23 AM
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See if your suction pump is disconnected. Happened to me and caused starting problems.
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Old 04-04-2011, 02:32 AM
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The rpm's are fine. It's just that if the engine is cold, you can floor it and get only a turtle crawl. Once warm, problem only occurs during wide turns.
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Old 04-05-2011, 10:10 PM
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During wide turns??????????

Fuel? does anyone else think it could possibly be a fuel pump?
How cold is it outside?

The turns thing is very confusing
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Old 07-22-2015, 04:44 PM
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Default Rough start when first starting in morning

Just had the Thermostat replaced on my daughters A4.
Changed all coils and plugs.
Now starts hard and very rough till warmed up.
Wondering if there is problem with the new thermostat?
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